Refrigeration systems consist of a refrigerant utilized in a cycle including a compressor, a condenser, an expansion valve and evaporator. While an expansion valve may potentially be as simple as an orifice, modern day refrigeration systems usually monitor the entire refrigeration cycle to optimize efficiency. Optimizing the efficiency in the condenser and in the evaporator entails providing an expansion valve having not only open and closed positions, but also a variety of partially open positions and a means for providing the correct optimum flow of refrigerant through the expansion valve. Presently known control apparatus used to operate a modulating expansion valve includes the use of an electric motor having an annular stator positioned on top of the valve and an armature positioned inside the hollow interior of the stator having a shaft in the center thereof which turns through a worm gear to raise and lower a regulating piston through the valve port. This type of motorized operator requires the use of shaft seals between the motor and the piston and thus provides an additional leak path to the atmosphere from the refrigeration system.
A need has arisen for an improved expansion valve for use in a refrigeration system that avoids the complexities of a motor operated expansion valve while providing simplicity of operation and a semi-hermetic seal between the valve and the atmosphere.